Airtight package including a package base and a glass cover hermetically sealed with each other via a sealing material layer

ABSTRACT

A hermetic package of the present invention includes a package base and a glass cover hermetically sealed with each other via a sealing material layer, wherein the package base includes a base part and a frame part formed on the base part, wherein the package base has an internal device housed within the frame part, wherein the sealing material layer is arranged between a top of the frame part of the package base and the glass cover, and wherein an end portion of the sealing material layer protrudes laterally in an arc shape in sectional view.

TECHNICAL FIELD

The present invention relates to a hermetic package, and morespecifically, to a hermetic package including a package base and a glasscover hermetically sealed with each other via a sealing material layer.

BACKGROUND ART

A hermetic package generally includes a package base, a glass coverhaving light transmissivity, and an internal device to be housed insidethereof.

There is a risk in that the internal device to be mounted in thehermetic package, such as a deep ultraviolet LED device, deterioratesowing to moisture penetrating from a surrounding environment. An organicresin-based adhesive having low-temperature curability has hitherto beenused for integrating the package base and the glass cover with eachother. However, the organic resin-based adhesive cannot completely blockmoisture or a gas, and hence there is a risk in that the internal devicedeteriorates with time.

Meanwhile, when composite powder including glass powder and refractoryfiller powder is used as a sealing material, the sealed sites are lessliable to deteriorate owing to moisture of a surrounding environment,and the hermetic reliability of the hermetic package is easily ensured.

However, the glass powder has a higher softening temperature than theorganic resin-based adhesive, and hence there is a risk in that theinternal device is thermally degraded at the time of sealing. Under suchcircumstances, laser sealing has attracted attention in recent years.According to the laser sealing, only a portion to be sealed can belocally heated, and hence the package base and the glass cover can behermetically integrated with each other without thermal degradation ofthe internal device.

CITATION LIST

Patent Literature 1: JP 2013-239609 A

Patent Literature 2: JP 2014-236202 A

SUMMARY OF INVENTION Technical Problem

Incidentally, when an excessive shear stress is applied to the hermeticpackage having been subjected to laser sealing, there is sometimes aproblem in that bulk fracture occurs in the sealing material layer, andthe hermetic reliability of the hermetic package cannot be ensured.

Thus, the present invention has been made in view of the above-mentionedcircumstances, and a technical object of the present invention is todevise a hermetic package in which bulk fracture is less liable to occurin a sealing material layer even when a shear stress is applied to thesealing material layer.

Solution to Problem

The inventors of the present invention have found that theabove-mentioned technical object can be achieved by causing an endportion of a sealing material layer to protrude in an arc shape. Thus,the finding is proposed as the present invention. That is, according toone embodiment of the present invention, there is provided a hermeticpackage, comprising a package base and a glass cover hermetically sealedwith each other via a sealing material layer, wherein the package basecomprises a base part and a frame part formed on the base part, whereinthe package base has an internal device housed within the frame part,wherein the sealing material layer is arranged between a top of theframe part of the package base and the glass cover, and wherein an endportion of the sealing material layer protrudes laterally in an arcshape in sectional view. The “arc shape” as used herein is not limitedto a complete arc shape, and means a convex shape which is rounded inits entirety with no corner.

In the hermetic package according to the embodiment of the presentinvention, the package base comprises the base part and the frame partformed on the base part, and the sealing material layer is arrangedbetween the top of the frame part of the package base and the glasscover. With this, the internal device, such as a deep ultraviolet LEDdevice, is easily housed within the frame part. Moreover, the internaldevice is less liable to deteriorate with time.

In addition, in the hermetic package according to the embodiment of thepresent invention, the end portion of the sealing material layer (aninner peripheral end portion and/or an outer peripheral end portion)protrudes laterally in an arc shape in sectional view. With this, when ashear stress is applied to the hermetic package, bulk fracture is lessliable to occur in the sealing material layer. As a result, the hermeticreliability of the hermetic package can be improved. Herein, when thesealing material layer is preliminarily formed on the glass cover, andthen the glass cover and the package base are laser sealed with eachother under a state in which the sealing material layer is pressed froma glass cover side, the end portion of the sealing material layer easilyprotrudes in an arc shape. In addition, when glass ceramic, alumina,aluminum nitride, or the like is used as the package base, the sealingmaterial layer exhibits appropriate wettability during laser sealing,and the end portion of the sealing material layer easily protrudes in anarc shape. The end portion of the sealing material layer generally has ameniscus shape (concave arc shape), or a shape in which a sealing widthbetween the glass cover and the sealing material layer is larger than asealing width (contact width) between the top of the frame part and thesealing material layer, that is, a shape which bulges from the top ofthe frame part toward the glass cover.

Secondly, in the hermetic package according to the embodiment of thepresent invention, it is preferred that a value obtained by dividing anaverage thickness of the sealing material layer by a maximum width ofthe sealing material layer be 0.003 or more. With this, even when alarge shear stress is applied to the sealing material layer, bulkfracture is less liable to occur in the sealing material layer. The“maximum width of the sealing material layer” generally refers to awidth of the sealing material layer corresponding to a portion whichprotrudes in an arc shape.

Thirdly, in the hermetic package according to the embodiment of thepresent invention, it is preferred that the sealing material layer beformed at a position distant from an inner peripheral end edge of thetop of the frame part and distant from an outer peripheral end edge ofthe top of the frame part.

Fourthly, in the hermetic package according to the embodiment of thepresent invention, it is preferred that an average thickness of thesealing material layer be less than 8.0 μm and a maximum width of thesealing material layer be from 1 μm to 1,000 μm.

Fifthly, in the hermetic package according to the embodiment of thepresent invention, it is preferred that the sealing material layercomprise a sintered body of composite powder containing at leastbismuth-based glass powder and refractory filler powder, and besubstantially free of a laser absorber. As compared to glasses based onother materials, bismuth-based glass has a feature of easily forming areaction layer in a surface layer of the package base (particularly, aceramic base) at the time of laser sealing. In addition, the refractoryfiller powder can increase the mechanical strength of the sealingmaterial layer, and can reduce the thermal expansion coefficient of thesealing material layer. Herein, the “bismuth-based glass” refers toglass comprising Bi₂O₃ as a main component, and specifically refers toglass comprising 25 mol % or more of Bi₂O₃ in a glass composition.

Sixthly, in the hermetic package according to the embodiment of thepresent invention, it is preferred that the package base comprise anyone of glass, glass ceramic, aluminum nitride, and aluminum oxide, or acomposite material thereof.

The present invention is described below with reference to the drawings.FIG. 1A is a schematic sectional view for illustrating an embodiment ofthe present invention, and FIG. 1B is an enlarged schematic sectionalview of a main portion F of the embodiment of the present invention. Ascan be seen from FIG. 1A, a hermetic package 1 comprises a package base10 and a glass cover 11. In addition, the package base 10 comprises abase part 12 and a frame part 13 in a frame shape on a peripheral endedge of the base part 12. Moreover, an internal device (e.g., deepultraviolet LED device) 14 is housed within the frame part 13 of thepackage base 10. Electrical wiring (not shown) configured toelectrically connect the internal device (e.g., deep ultraviolet LEDdevice) 14 to an outside is formed in the package base 10.

A sealing material layer 15 is arranged between a top of the frame part13 of the package base 10 and a surface of the glass cover 11 on aninternal device 14 side over the entire periphery of the top of theframe part. In addition, the sealing material layer 15 comprisesbismuth-based glass and refractory filler powder, and is substantiallyfree of a laser absorber. Moreover, the width of the sealing materiallayer 15 is smaller than the width of the frame part 13 of the packagebase 10, and further, the sealing material layer 15 is distant from anend edge of the glass cover 11. Further, the average thickness of thesealing material layer 15 is less than 8.0 μm.

As apparent from FIG. 1B, an inner peripheral end portion 16 of thesealing material layer 15 protrudes in an arc shape, and an outerperipheral end portion 17 of the sealing material layer 15 protrudes inan arc shape. In other words, the sealing material layer 15 bulges in anX direction in sectional view. Moreover, a portion of the sealingmaterial layer 15 which has a maximum width corresponds to a portionwhich protrudes in an arc shape (vertex of a bulged portion). That is, awidth A of the sealing material layer 15 corresponding to the portionwhich protrudes in an arc shape is larger than a sealing width B(contact width) between the top of the frame part 13 and the sealingmaterial layer 15, and is also larger than a sealing width C (contactwidth) between the glass cover 11 and the sealing material layer 15.

The sealing width B (contact width) between the top of the frame part 13and the sealing material layer 15 is preferably larger than the sealingwidth C (contact width) between the glass cover 11 and the sealingmaterial layer 15 from the viewpoint of accuracy of laser sealing.Meanwhile, the sealing width B (contact width) between the top of theframe part 13 and the sealing material layer 15 is preferably smallerthan the sealing width C (contact width) between the glass cover 11 andthe sealing material layer 15 from the viewpoint of sealing strength.

In addition, the above-mentioned hermetic package 1 may be produced asdescribed below. First, the glass cover 11 on which the sealing materiallayer 15 has been formed in advance is placed on the package base 10 sothat the sealing material layer 15 and the top of the frame part 13 arebrought into contact with each other. Subsequently, while the glasscover 11 is pressed with a pressing jig, laser light L output from alaser irradiation apparatus 18 is radiated along the sealing materiallayer 15 from a glass cover 11 side. With this, the sealing materiallayer 15 softens and flows to react with a surface layer on the top ofthe frame part 13 of the package base 10, to thereby hermeticallyintegrate the package base 10 and the glass cover 11 with each other.Thus, a hermetic structure of the hermetic package 1 is formed. Inaddition, the sealing material layer 15 is pressed from above during itssoftening and flowing, and thus the inner peripheral end portion 16 andthe outer peripheral end portion 17 of the sealing material layer 15each protrude in an arc shape. It is also appropriate to preliminarilyform the sealing material layer 15 on the top of the frame part 13 ofthe package base 10 instead of preliminarily forming the sealingmaterial layer 15 on the glass cover 11.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic sectional view for illustrating an embodiment ofthe present invention.

FIG. 1B is an enlarged schematic sectional view of a main portion of theembodiment of the present invention.

FIG. 2 is a schematic view for illustrating a softening point ofcomposite powder measured with a macro-type DTA apparatus.

FIG. 3 is a sectional micrograph for showing the shape of an innerperipheral end portion of a sealing material layer according to Example.

FIG. 4 is a sectional micrograph for showing the shape of an outerperipheral end portion of the sealing material layer according toExample.

DESCRIPTION OF EMBODIMENTS

As described above, a hermetic package of the present inventioncomprises a package base and a glass cover hermetically sealed with eachother via a sealing material layer, wherein the package base comprises abase part and a frame part formed on the base part, wherein the packagebase has an internal device housed within the frame part, wherein thesealing material layer is arranged between a top of the frame part ofthe package base and the glass cover, and wherein an end portion of thesealing material layer protrudes laterally in an arc shape in sectionalview. The hermetic package of the present invention is described indetail below.

In the hermetic package of the present invention, the package basecomprises the base part and the frame part formed on the base part. Withthis, the internal device, such as a deep ultraviolet LED device, iseasily housed within the frame part of the package base. The frame partof the package base is preferably formed in a frame shape along an outerperipheral end edge region of the package base. With this, an effectivearea for functioning as a device can be enlarged. In addition, theinternal device, such as a deep ultraviolet LED device, is easily housedwithin the frame part of the package base. Besides, for example, joiningof wiring is easily performed.

On the top of the frame part, a surface of a region in which the sealingmaterial layer is to be formed preferably has a surface roughness Ra ofless than 1.0 μm. When the surface roughness Ra on the surface isincreased, the accuracy of laser sealing is liable to be reduced.Herein, the “surface roughness Ra” may be measured with, for example, acontact-type or non-contact-type laser film thickness meter or surfaceroughness meter.

The width of the top of the frame part is preferably from 100 μm to3,000 μm or from 200 μm to 1,500 μm, particularly preferably from 300 μmto 900 μm. When the width of the top of the frame part is too small, itbecomes difficult to align the sealing material layer and the top of theframe part. Meanwhile, when the width of the top of the frame part istoo large, the effective area for functioning as a device is reduced.

The package base is preferably formed of any one of glass, glassceramic, aluminum nitride, and aluminum oxide, or a composite materialthereof (e.g., a composite material in which aluminum nitride and glassceramic are integrated with each other). Glass easily forms a reactionlayer with the sealing material layer, and hence high sealing strengthcan be ensured through the laser sealing. Glass ceramic has a feature ofeasily exhibiting appropriate wettability to the sealing material layer,and hence facilitating formation of a protrusion in an arc shape at theend portion of the sealing material layer. Further, glass ceramicfacilitates formation of a thermal via, and hence a situation in whichthe temperature of the hermetic package is excessively increased can beproperly prevented. Aluminum nitride and aluminum oxide each have afeature of easily exhibiting appropriate wettability to the sealingmaterial layer, and hence facilitating formation of a protrusion in anarc shape at the end portion of the sealing material layer. Further,aluminum nitride and aluminum oxide each have a satisfactory heatdissipating property, and hence a situation in which the temperature ofthe hermetic package is excessively increased can be properly prevented.

It is preferred that glass ceramic, aluminum nitride, and aluminum oxideeach have dispersed therein a black pigment (be each sintered under astate in which a black pigment is dispersed therein). With this, thepackage base can absorb laser light having transmitted through thesealing material layer. As a result, a portion of the package base to bebrought into contact with the sealing material layer is heated duringthe laser sealing, and hence the formation of the reaction layer can bepromoted at an interface between the sealing material layer and thepackage base.

The package base having dispersed therein the black pigment preferablyhas a property of absorbing laser light to be radiated, that is, has atotal light transmittance at the wavelength (808 nm) of the laser lightto be radiated of 10% or less (desirably 5% or less) when having athickness of 0.5 mm. With this, the temperature of the sealing materiallayer is easily increased at an interface between the package base andthe sealing material layer.

The thickness of the base part of the package base is preferably from0.1 mm to 2.5 mm, particularly preferably from 0.2 mm to 1.5 mm. Withthis, thinning of the hermetic package can be achieved.

The height of the frame part of the package base, that is, a heightobtained by subtracting the thickness of the base part from the packagebase is preferably from 100 μm to 2,000 μm, particularly preferably from200 μm to 900 μm. With this, thinning of the hermetic package is easilyachieved while the internal device is properly housed therein.

Various glasses may be used for the glass cover. For example,alkali-free glass, alkali borosilicate glass, or soda lime glass may beused. The glass cover may be laminated glass obtained by bonding aplurality of glass sheets.

A functional film may be formed on a surface of the glass cover on aninternal device side, or on a surface of the glass cover on an outside.An antireflection film is particularly preferred as the functional film.With this, light reflected on the surface of the glass cover can bereduced.

The thickness of the glass cover is preferably 0.1 mm or more, from 0.2mm to 2.0 mm, or from 0.4 mm to 1.5 mm, particularly preferably from 0.5mm to 1.2 mm. When the thickness of the glass cover is small, thestrength of the hermetic package is liable to be reduced. Meanwhile,when the thickness of the glass cover is large, it becomes difficult toachieve thinning of the hermetic package.

A difference in thermal expansion coefficient between the glass coverand the sealing material layer is preferably less than 50×10⁻⁷/° C. orless than 40×10⁻⁷/° C., particularly preferably 30×10⁻⁷/° C. or less.When the difference in thermal expansion coefficient is too large, astress remaining in the sealed sites is improperly increased, and thehermetic reliability of the hermetic package is liable to be reduced.

The sealing material layer has a function of softening and deforming byabsorbing laser light to form a reaction layer in a surface layer of thepackage base, to thereby hermetically integrate the package base and theglass cover with each other.

The end portion of the sealing material layer (an inner peripheral endportion and/or an outer peripheral end portion) protrudes laterally inan arc shape in sectional view. It is preferred that the innerperipheral end portion and the outer peripheral end portion of thesealing material layer protrude in an arc shape. With this, when a shearstress is applied to the hermetic package, bulk fracture is less liableto occur in the sealing material layer. As a result, the hermeticreliability of the hermetic package can be improved.

A maximum protrusion width of the sealing material layer (the total of amaximum bulge width at the inner peripheral end portion and a maximumbulge width at the outer peripheral end portion) is larger than anaverage sealing width (average contact width) between the top of theframe part and the sealing material layer by preferably 0.2 μm or more(A-B in FIG. 1B), particularly preferably 0.5 μm or more. The maximumprotrusion width (the total of the maximum bulge width at the innerperipheral end portion and the maximum bulge width at the outerperipheral end portion) is larger than an average sealing width (averagecontact width) between the glass cover and the sealing material layer bypreferably 0.2 μm or more (A-C in FIG. 1B), particularly preferably 0.5μm or more. With this, when a shear stress is applied to the hermeticpackage, bulk fracture is less liable to occur in the sealing materiallayer. As a result, the hermetic reliability of the hermetic package canbe properly improved.

The maximum protrusion width at the inner peripheral end portion of thesealing material layer (the maximum bulge width at the inner peripheralend portion) is larger than the average sealing width (average contactwidth) between the top of the frame part and the sealing material layerby preferably 0.1 μm or more or 0.3 μm or more, particularly preferably0.5 μm or more. The maximum protrusion width at the inner peripheral endportion (the maximum bulge width at the inner peripheral end portion) islarger than the average sealing width (average contact width) betweenthe glass cover and the sealing material layer by preferably 0.1 μm ormore or 0.3 μm or more, particularly preferably 0.5 μm or more. Withthis, when a shear stress is applied to an inside of the hermeticpackage, bulk fracture is less liable to occur in the sealing materiallayer. As a result, the hermetic reliability of the hermetic package canbe properly improved.

The maximum protrusion width at the outer peripheral end portion of thesealing material layer (the maximum bulge width at the outer peripheralend portion) is larger than the average sealing width (average contactwidth) between the top of the frame part and the sealing material layerby preferably 0.1 μm or more or 0.3 μm or more, particularly preferably0.5 μm or more. The maximum protrusion width at the outer peripheral endportion (the maximum bulge width at the outer peripheral end portion) islarger than the average sealing width (average contact width) betweenthe glass cover and the sealing material layer by preferably 0.1 μm ormore or 0.3 μm or more, particularly preferably 0.5 μm or more. Withthis, when a shear stress is applied to an outside of the hermeticpackage, bulk fracture is less liable to occur in the sealing materiallayer. As a result, the hermetic reliability of the hermetic package canbe properly improved.

The sealing material layer is preferably formed so that its contactposition with the frame part is distant from the inner peripheral endedge of the top of the frame part and distant from the outer peripheralend edge of the top of the frame part. The sealing material layer ismore preferably formed at a position distant from the inner peripheralend edge of the top of the frame part by 50 μm or more, 60 μm or more,or from 70 μm to 2,000 μm, particularly from 80 μm to 1,000 μm. When adistance between the inner peripheral end edge of the top of the framepart and the sealing material layer is too short, it becomes difficultto release heat generated through local heating during the lasersealing, and hence the glass cover is liable to be broken in the courseof cooling. Meanwhile, when the distance between the inner peripheralend edge of the top of the frame part and the sealing material layer istoo long, it becomes difficult to achieve downsizing of the hermeticpackage. In addition, the sealing material layer is preferably formed ata position distant from the outer peripheral end edge of the top of theframe part by 50 μm or more, 60 μm or more, or from 70 μm to 2,000 μm,particularly from 80 μm to 1,000 μm. When a distance between the outerperipheral end edge of the top of the frame part and the sealingmaterial layer is too short, it becomes difficult to release heatgenerated through local heating during the laser sealing, and hence theglass cover is liable to be broken in the course of cooling. Meanwhile,when the distance between the outer peripheral end edge of the top ofthe frame part and the sealing material layer is too long, it becomesdifficult to achieve downsizing of the hermetic package.

The sealing material layer is preferably formed so that its contactposition with the glass cover is distant from an end edge of the glasscover by 50 μm or more, 60 μm or more, or from 70 μm to 1, 500 μm,particularly from 80 μm to 800 μm. When a distance between the end edgeof the glass cover and the sealing material layer is too short, adifference in surface temperature between the surface of the glass coveron the internal device side and the surface of the glass cover on theoutside is increased in an end edge region of the glass cover at thetime of laser sealing, and the glass cover is liable to be broken.

The sealing material layer is preferably formed on a center line of thetop of the frame part in a width direction, that is, in a middle regionof the top of the frame part. With this, heat generated through localheating during the laser sealing is easily released, and hence the glasscover is less liable to be broken. When the top of the frame part has asufficiently large width, the sealing material layer does not need to beformed on the center line of the top of the frame part in the widthdirection.

The average thickness of the sealing material layer is preferably lessthan 8.0 μm, particularly preferably 1.0 μm or more and less than 6.0μm. As the average thickness of the sealing material layer is reducedmore, a stress remaining in the sealed sites after the laser sealing canbe reduced more when the thermal expansion coefficient of the sealingmaterial layer and the thermal expansion coefficient of the glass coverdo not match each other. In addition, also the accuracy of the lasersealing can be improved more. As a method of controlling the averagethickness of the sealing material layer as described above, thefollowing methods are given: a method involving thinly applying acomposite powder paste; and a method involving subjecting the surface ofthe sealing material layer to polishing treatment.

The maximum width of the sealing material layer is preferably 1 μm ormore and 2,000 μm or less, 10 μm or more and 1,000 μm or less, or 50 μmor more and 800 μm or less, particularly preferably 100 μm or more and600 μm or less. When the maximum width of the sealing material layer issmall, the sealing material layer is easily distant from the end edgesof the frame part, and hence a stress remaining in the sealed sitesafter the laser sealing is easily reduced. Further, the width of theframe part of the package base can be reduced, and thus the effectivearea for functioning as a device can be enlarged. Meanwhile, when themaximum width of the sealing material layer is too small, bulk fractureis liable to occur in the sealing material layer in the case where alarge shear stress is applied to the sealing material layer. Further,the accuracy of laser sealing is liable to be reduced.

A value obtained by dividing the average thickness of the sealingmaterial layer by the maximum width of the sealing material layer ispreferably 0.003 or more, 0.005 or more, or from 0.01 to 0.1,particularly preferably from 0.02 to 0.05. When the value obtained bydividing the average thickness of the sealing material layer by themaximum width of the sealing material layer is too small, bulk fractureis liable to occur in the sealing material layer in the case where alarge shear stress is applied to the sealing material layer. Meanwhile,when the value obtained by dividing the average thickness of the sealingmaterial layer by the maximum width of the sealing material layer is toolarge, the accuracy of laser sealing is liable to be reduced.

The surface roughness Ra of the sealing material layer is preferablyless than 0.5 μm or 0.2 μm or less, particularly preferably from 0.01 μmto 0.15 μm. In addition, the surface roughness RMS of the sealingmaterial layer is preferably less than 1.0 μm or 0.5 μm or less,particularly preferably from 0.05 μm to 0.3 μm. With this, theadhesiveness between the package base and the sealing material layer isincreased, and the accuracy of the laser sealing is improved. Herein,the “surface roughness RMS” may be measured with, for example, acontact-type or non-contact-type laser film thickness meter or surfaceroughness meter. As a method of controlling the surface roughnesses Raand RMS of the sealing material layer as described above, the followingmethods are given: a method involving subjecting the surface of thesealing material layer to polishing treatment; and a method involvingreducing the particle size of refractory filler powder.

The sealing material layer preferably comprises a sintered body ofcomposite powder containing at least glass powder and refractory fillerpowder. The glass powder is a component which absorbs laser light duringthe laser sealing to soften and deform, to thereby hermeticallyintegrate the package base and the glass cover with each other. Therefractory filler powder is a component which acts as a frameworkmaterial, and increases the mechanical strength of the sealing materiallayer while reducing the thermal expansion coefficient of the sealingmaterial layer. The sealing material layer may comprise a laser absorberin order to improve light absorption characteristics in addition to theglass powder and the refractory filler powder.

Various materials may be used as the composite powder. Of those,composite powder containing bismuth-based glass powder and refractoryfiller powder is preferably used from the viewpoint of increasingsealing strength. As the composite powder, it is preferred to usecomposite powder containing 55 vol % to 95 vol % of bismuth-based glasspowder and 5 vol % to 45 vol % of refractory filler powder. It is morepreferred to use composite powder containing 60 vol % to 85 vol % ofbismuth-based glass powder and 15 vol % to 40 vol % of refractory fillerpowder. It is particularly preferred to use composite powder containing60 vol % to 80 vol % of bismuth-based glass powder and 20 vol % to 40vol % of refractory filler powder. When the refractory filler powder isadded, the thermal expansion coefficient of the sealing material layereasily matches the thermal expansion coefficients of the glass cover andthe package base. As a result, a situation in which an improper stressremains in the sealed sites after the laser sealing is easily prevented.Meanwhile, when the content of the refractory filler powder is toolarge, the content of the glass powder is relatively reduced. Thus, thesurface smoothness of the sealing material layer is reduced, and theaccuracy of the laser sealing is liable to be reduced.

The softening point of the composite powder is preferably 510° C. orless or 480° C. or less, particularly preferably 450° C. or less. Whenthe softening point of the composite powder is too high, it becomesdifficult to increase the surface smoothness of the sealing materiallayer. The lower limit of the softening point of the composite powder isnot particularly set, but in consideration of the thermal stability ofthe glass powder, the softening point of the composite powder ispreferably 350° C. or more. Herein, the “softening point” refers to thefourth inflection point measured with a macro-type DTA apparatus, andcorresponds to Ts in FIG. 2 .

The bismuth-based glass preferably comprises as a glass composition, interms of mol %, 28% to 60% of Bi₂O₃, 15% to 37% of B₂O₃, and 1% to 30%of ZnO. The reasons why the content range of each component is limitedas described above are described below. In the description of the glasscomposition range, the expression “%” means “mol %”.

Bi₂O₃ is a main component for reducing a softening point. The content ofBi₂O₃ is preferably from 28% to 60% or from 33% to 55%, particularlypreferably from 35% to 45%. When the content of Bi₂O₃ is too small, thesoftening point becomes too high, and softening flowability is liable tobe reduced. Meanwhile, when the content of Bi₂O₃ is too large, the glassis liable to devitrify at the time of laser sealing, and owing to thedevitrification, the softening flowability is liable to be reduced.

B₂O₃ is an essential component as a glass-forming component. The contentof B₂O₃ is preferably from 15% to 37% or from 19% to 33%, particularlypreferably from 22% to 30%. When the content of B₂O₃ is too small, aglass network is hardly formed, and hence the glass is liable todevitrify at the time of laser sealing. Meanwhile, when the content ofB₂O₃ is too large, the glass has increased viscosity, and hence thesoftening flowability is liable to be reduced.

ZnO is a component which improves devitrification resistance. Thecontent of ZnO is preferably from 1% to 30%, from 3% to 25%, or from 5%to 22%, particularly preferably from 5% to 20%. When the content of ZnOis outside the above-mentioned range, the glass composition loses itscomponent balance, and hence the devitrification resistance is liable tobe reduced contrarily.

In addition to the above-mentioned components, for example, thefollowing components may be added.

SiO₂ is a component which improves water resistance. The content of SiO₂is preferably from 0% to 5%, from 0% to 3%, or from 0% to 2%,particularly preferably from 0% to 1%. When the content of SiO₂ is toolarge, there is a risk in that the softening point is improperlyincreased. In addition, the glass is liable to devitrify at the time oflaser sealing.

Al₂O₃ is a component which improves the water resistance. The content ofAl₂O₃ is preferably from 0% to 10% or from 0.1% to 5%, particularlypreferably from 0.5% to 3%. When the content of Al₂O₃ is too large,there is a risk in that the softening point is improperly increased.

Li₂O, Na₂O, and K₂O are each a component which reduces thedevitrification resistance. Therefore, the content of each of Li₂O,Na₂O, and K₂O is preferably from 0% to 5% or from 0% to 3%, particularlypreferably from 0% to less than 1%.

MgO, CaO, SrO, and BaO are each a component which improves thedevitrification resistance, but are each a component which increases thesoftening point. Therefore, the content of each of MgO, CaO, SrO, andBaO is preferably from 0% to 20% or from 0% to 10%, particularlypreferably from 0% to 5%.

In order to reduce the softening point of bismuth-based glass, it isrequired to introduce a large amount of Bi₂O₃ into the glasscomposition, but when the content of Bi₂O₃ is increased, the glass isliable to devitrify at the time of laser sealing, and owing to thedevitrification, the softening flowability is liable to be reduced. Thistendency is particularly remarkable when the content of Bi₂O₃ is 30% ormore. As a countermeasure for this problem, the addition of CuO caneffectively suppress a reduction in devitrification resistance even whenthe content of Bi₂O₃ is 30% or more. Further, when CuO is added, laserabsorption characteristics at the time of laser sealing can be improved.The content of CuO is preferably from 0% to 40%, from 1% to 40%, from 5%to 35%, or from 10% to 30%, particularly preferably from 13% to 25%.When the content of CuO is too large, the glass composition loses itscomponent balance, and hence the devitrification resistance is liable tobe reduced contrarily. In addition, the total light transmittance of thesealing material layer is excessively reduced, and it becomes difficultto locally heat a boundary region between the package base and thesealing material layer.

Fe₂O₃ is a component which improves the devitrification resistance andthe laser absorption characteristics. The content of Fe₂O₃ is preferablyfrom 0% to 10% or from 0.1% to 5%, particularly preferably from 0.4% to2%. When the content of Fe₂O₃ is too large, the glass composition losesits component balance, and hence the devitrification resistance isliable to be reduced contrarily.

MnO is a component which improves the laser absorption characteristics.The content of MnO is preferably from 0% to 25%, particularly preferablyfrom 5% to 15%. When the content of MnO is too large, thedevitrification resistance is liable to be reduced.

Sb₂O₃ is a component which improves the devitrification resistance. Thecontent of Sb₂O₃ is preferably from 0% to 5%, particularly preferablyfrom 0% to 2%. When the content of Sb₂O₃ is too large, the glasscomposition loses its component balance, and hence the devitrificationresistance is liable to be reduced contrarily.

The average particle diameter D₅₀ of the glass powder is preferably lessthan 15 μm or from 0.5 μm to 10 μm, particularly preferably from 1 μm to5 μm. As the average particle diameter D₅₀ of the glass powder becomessmaller, the softening point of the glass powder is reduced more.Herein, the “average particle diameter D₅₀” refers to a value measuredby laser diffractometry on a volume basis.

The refractory filler powder is preferably one kind or two or more kindsselected from cordierite, zircon, tin oxide, niobium oxide, zirconiumphosphate-based ceramic, willemite, β-eucryptite, and β-quartz solidsolution, particularly preferably β-eucryptite or cordierite. Thoserefractory filler powders each have a low thermal expansion coefficientand a high mechanical strength, and besides are each well compatiblewith the bismuth-based glass.

The average particle diameter D₅₀ of the refractory filler powder ispreferably less than 2 μm, particularly preferably 0.1 μm or more andless than 1.5 μm. When the average particle diameter D₅₀ of therefractory filler powder is too large, the surface smoothness of thesealing material layer is liable to be reduced. Besides, the averagethickness of the sealing material layer is liable to be increased, withthe result that the accuracy of the laser sealing is liable to bereduced.

The 99% particle diameter D₉₉ of the refractory filler powder ispreferably less than 5 μm or 4 μm or less, particularly preferably 0.3μm or more and 3 μm or less. When the 99% particle diameter D₉₉ of therefractory filler powder is too large, the surface smoothness of thesealing material layer is liable to be reduced. Besides, the averagethickness of the sealing material layer is liable to be increased, withthe result that the accuracy of the laser sealing is liable to bereduced. Herein, the “99% particle diameter D₉₉” refers to a valuemeasured by laser diffractometry on a volume basis.

The sealing material layer may further comprise a laser absorber inorder to improve light absorption characteristics. However, the laserabsorber has an action of accelerating the devitrification of thebismuth-based glass, and hence, the content of the laser absorber in thesealing material layer is preferably 10 vol % or less, 5 vol % or less,1 vol % or less, or 0.5 vol % or less. It is particularly preferred thatthe sealing material layer be substantially free of the laser absorber(0.1 vol % or less). When the bismuth-based glass has satisfactorydevitrification resistance, the laser absorber may be introduced at 1vol % or more, particularly 3 vol % or more in order to improve laserabsorption characteristics. As the laser absorber, for example, aCu-based oxide, an Fe-based oxide, a Cr-based oxide, a Mn-based oxide,or a spinel-type composite oxide thereof may be used.

The thermal expansion coefficient of the sealing material layer ispreferably from 55×10⁻⁷/° C. to 95×10⁻⁷/° C. or from 60×10⁻⁷/° C. to82×10⁻⁷/° C., particularly preferably from 65×10⁻⁷/° C. to 76×10⁻⁷/° C.With this, the thermal expansion coefficient of the sealing materiallayer matches the thermal expansion coefficient of the glass cover orthe thermal expansion coefficient of the package base, with the resultthat bulk fracture due to a shear stress is less liable to occur in thesealing material layer. The “thermal expansion coefficient” refers to avalue measured with a push-rod type thermal expansion coefficientmeasurement (TMA) apparatus in a temperature range of from 30° C. to300° C.

The sealing material layer may be formed by various methods. Of those,the sealing material layer is preferably formed by a method involvingapplying and sintering a composite powder paste. Moreover, theapplication of the composite powder paste is preferably performed with acoating machine, such as a dispenser or a screen printing machine. Withthis, the dimensional accuracy of the sealing material layer (thedimensional accuracy of the sealing material layer in terms of width)can be improved. In this case, the composite powder paste is a mixtureof the composite powder and a vehicle. In addition, the vehiclegenerally contains a solvent and a resin. The resin is added for thepurpose of adjusting the viscosity of the paste. In addition, asurfactant, a thickener, or the like may also be added thereto asrequired.

The composite powder paste is generally produced by kneading thecomposite powder and the vehicle with a triple roller or the like. Thevehicle generally contains a resin and a solvent. As the resin to beused in the vehicle, there may be used an acrylic acid ester (acrylicresin), ethylcellulose, a polyethylene glycol derivative,nitrocellulose, polymethylstyrene, polyethylene carbonate, polypropylenecarbonate, a methacrylic acid ester, and the like. As the solvent to beused in the vehicle, there may be used N,N′-dimethyl formamide (DMF),α-terpineol, a higher alcohol, γ-butyrolactone (γ-BL), tetralin,butylcarbitol acetate, ethyl acetate, isoamyl acetate, diethylene glycolmonoethyl ether, diethylene glycol monoethyl ether acetate, benzylalcohol, toluene, 3-methoxy-3-methylbutanol, triethylene glycolmonomethyl ether, triethylene glycol dimethyl ether, dipropylene glycolmonomethyl ether, dipropylene glycol monobutyl ether, tripropyleneglycol monomethyl ether, tripropylene glycol monobutyl ether, propylenecarbonate, dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone, and thelike.

The composite powder paste may be applied onto the top of the frame partof the package base, but is preferably applied in a frame shape alongthe peripheral end edge region of the glass cover. With this, thesealing material layer does not need to be seized to the package base,and thermal degradation of the internal device, such as a deepultraviolet LED device, can be suppressed.

As a method of producing the hermetic package of the present invention,it is preferred to radiate laser light to the sealing material layerfrom a glass cover side to soften and deform the sealing material layer,to thereby hermetically seal the package base and the glass cover witheach other to obtain a hermetic package. In this case, the glass covermay be arranged below the package base, but from the viewpoint of theefficiency of the laser sealing, the glass cover is preferably arrangedabove the package base.

Various lasers may be used as the laser. In particular, a semiconductorlaser, a YAG laser, a CO₂ laser, an excimer laser, and an infrared laserare preferred because those lasers are easy to handle.

An atmosphere for performing the laser sealing is not particularlylimited. An air atmosphere or an inert atmosphere, such as a nitrogenatmosphere, may be adopted.

At the time of laser sealing, when the glass cover is preheated at atemperature equal to or higher than 100° C. and equal to or lower thanthe temperature limit of the internal device, the breakage of the glasscover due to thermal shock at the time of laser sealing is easilysuppressed. In addition, when an annealing laser is radiated from theglass cover side immediately after the laser sealing, the breakage ofthe glass cover due to thermal shock or a residual stress is more easilysuppressed.

The laser sealing is preferably performed under a state in which theglass cover is pressed. With this, the end portion of the sealingmaterial layer easily protrudes in an arc shape at the time of lasersealing.

EXAMPLES

Now, the present invention is described in detail by way of Examples.The following Examples are merely illustrative. The present invention isby no means limited to the following Examples.

First, bismuth-based glass powder and refractory filler powder weremixed at a ratio of 90.0 mass %:10.0 mass % to produce composite powder.In this case, the bismuth-based glass powder had an average particlediameter D₅₀ of 1.0 μm and a 99% particle diameter D₉₉ of 2.5 μm, andthe refractory filler powder had an average particle diameter D₅₀ of 1.0μm and a 99% particle diameter D₉₉ of 2.5 μm. The bismuth-based glasscomprises as a glass composition, in terms of mol %, 39% of Bi₂O₃, 23.7%of B₂O₃, 14.1% of ZnO, 2.7% of Al₂O₃, 20% of CuO, and 0.6% of Fe₂O₃. Inaddition, the refractory filler powder is β-eucryptite.

The obtained composite powder was measured for a thermal expansioncoefficient. As a result, it was found that the thermal expansioncoefficient was 71×10⁻⁷/° C. The thermal expansion coefficient is avalue measured with a push-rod type TMA apparatus in a measurementtemperature range of from 30° C. to 300° C.

Next, through use of the composite powder, a sealing material layer in aframe shape was formed at a position distant from an end edge of a glasscover made of borosilicate glass (measuring 4.0 mm in length×4.0 mm inwidth×0.15 mm in thickness) by about 100 μm. Specifically, first, theabove-mentioned composite powder, a vehicle, and a solvent were kneadedso as to achieve a viscosity of about 100 Pa·s (25° C., shear rate: 4),and then further kneaded with a triple roll mill until powders werehomogeneously dispersed, and formed into a paste. Thus, a compositepowder paste was obtained. A vehicle obtained by dissolving an ethylcellulose resin in a glycol ether-based solvent was used as the vehicle.Next, the above-mentioned composite powder paste was printed in a frameshape with a screen printing machine along the peripheral end edge ofthe glass cover. Further, the composite powder paste was dried at 120°C. for 10 minutes under an air atmosphere, and then fired at 500° C. for10 minutes under an air atmosphere. Thus, a sealing material layer wasformed on the glass cover.

In addition, a package base formed of glass ceramic (measuring 4.0 mm inlength×4.0 mm in width×0.8 mm in thickness of a base part) was prepared.A frame part is formed in a frame shape on the peripheral end edge ofthe package base. Moreover, the package base had a surface roughness Raof from 0.1 μm to 1.0 μm. The glass ceramic is formed by sintering alaminate of green sheets each containing the glass powder and therefractory filler powder.

Finally, the package base and the glass cover were arranged so as to belaminated on each other so that a top of the frame part of the packagebase and the sealing material layer were brought into contact with eachother. After that, while the glass cover was pressed with a pressingjig, a semiconductor laser having a wavelength of 808 nm, an output of 4W, and an irradiation diameter of 0.5 mm was radiated at an irradiationspeed of 15 mm/sec to the sealing material layer from a glass cover sideto soften and deform the sealing material layer, to thereby hermeticallyintegrate the package base and the glass cover with each other. Thus, ahermetic package was obtained. The average thickness of the sealingmaterial layer was 5.0 μm, and the maximum width of the sealing materiallayer was 200 μm.

In the resultant hermetic package, a sectional surface of an end portionof the sealing material layer was exposed by ion milling. A sectionalmicrograph for showing the shape of an inner peripheral end portion ofthe sealing material layer is shown in FIG. 3 , and a sectionalmicrograph for showing the shape of an outer peripheral end portion ofthe sealing material layer is shown in FIG. 4 . In each of FIG. 3 andFIG. 4 , the glass cover is arranged at an upper side, and the top ofthe frame part of the package base is arranged at a lower side. Asapparent from FIG. 3 and FIG. 4 , in the resultant hermetic package, theinner peripheral end portion of the sealing material layer protruded inan arc shape in sectional view, and the outer peripheral end portion ofthe sealing material layer also protruded in an arc shape. Therefore, itis considered that, in the resultant hermetic package, bulk fracture dueto a shear stress is less liable to occur in the sealing material layer.

The resultant hermetic package was evaluated for cracks and hermeticreliability after the laser sealing. First, the sealed sites wereobserved with an optical microscope. As a result, the generation ofcracks was not observed. Next, the resultant hermetic package wassubjected to a pressure cooker test (highly accelerated temperature andhumidity stress test: HAST test), and then, the neighborhood of thesealing material layer was observed. As a result, transformation,cracks, peeling, and the like were not observed at all. The conditionsof the HAST test are 121° C., a humidity of 100%, 2 atm, and 24 hours.

INDUSTRIAL APPLICABILITY

The hermetic package of the present invention is suitable as a hermeticpackage having mounted therein an internal device, such as a sensor chipor a deep ultraviolet LED device. Other than the above, the hermeticpackage of the present invention is also suitably applicable to ahermetic package having housed therein, for example, a piezoelectricvibration device, or a wavelength conversion device in which quantumdots are dispersed in a resin.

REFERENCE SIGNS LIST

-   -   1 hermetic package    -   10 package base    -   11 glass cover    -   12 base part    -   13 frame part    -   14 internal device (e.g., deep ultraviolet LED device)    -   15 sealing material layer    -   16 inner peripheral end portion of sealing material layer    -   17 outer peripheral end portion of sealing material layer    -   18 laser irradiation apparatus    -   L laser light

The invention claimed is:
 1. A hermetic package comprising a packagebase and a glass cover hermetically sealed with each other via a sealingmaterial layer, wherein the package base comprises a base part and aframe part formed on the base part, wherein the package base has aninternal device housed within the frame part, wherein the sealingmaterial layer is arranged between a top of the frame part of thepackage base and the glass cover, wherein an end portion of the sealingmaterial layer protrudes laterally in an arc shape in sectional view,wherein the sealing material layer comprises a sintered body ofcomposite powder containing at least bismuth-based glass powder andrefractory filler powder, and wherein the bismuth-based glass powdercomprises as a glass composition, in terms of mol %, 28% to 60% ofBi₂O₃, 0% of BaO, 15% to 37% of B₂O₃, 1% to 30% of ZnO, 1% to 40% ofCuO, and 0.1% to 10% of Fe₂O₃.
 2. The hermetic package according toclaim 1, wherein a value obtained by dividing an average thickness ofthe sealing material layer by a maximum width of the sealing materiallayer is 0.003 or more.
 3. The hermetic package according to claim 1,wherein the sealing material layer is formed at a position distant froman inner peripheral end edge of the top of the frame part and distantfrom an outer peripheral end edge of the top of the frame part.
 4. Thehermetic package according to claim 1, wherein an average thickness ofthe sealing material layer is less than 8.0 μm and a maximum width ofthe sealing material layer is from 1 μm to 1,000 μm.
 5. The hermeticpackage according to claim 1, wherein the sealing material layer issubstantially free of a laser absorber.
 6. The hermetic packageaccording to claim 1, wherein the package base comprises any one ofglass, glass ceramic, aluminum nitride, and aluminum oxide, or acomposite material thereof.